The freshman senator surprised few people Wednesday with his announcement that he will not seek reelection next year. Senator Webb had not raised much money and was not an enthusiastic campaigner. But it’s usually easier for an incumbent to win than a newcomer – especially in a state where the Republicans rebounded in 2009 and 2010.

Plus, Virginia Democrats don’t have a big bench. Their best hope – former Gov. Tim Kaine, chairman of the Democratic National Committee – has said in the past he’s not interested in running for the Senate. Now that the seat is open, there’s speculation President Obama may twist his arm. For Mr. Obama to win Virginia again in 2012, it will be less difficult if a strong Democrat is on the Senate line.

In a statement on Webb’s retirement, Mr. Kaine did not discuss his own intentions.

"[O]ver the past decade, we’ve made major progress in turning Virginia from a solidly Republican state to a highly competitive one, including Senator Webb’s victory in 2006, Senator Warner’s victory in 2008, and President Obama’s historic victory in 2008," Kaine said. "With the investments that President Obama and the Democratic Party will make in Virginia in 2012, I am confident that our party will hold on to this Senate seat in 2012.”

In 2008, Obama became the first Democratic presidential candidate to win the Old Dominion since 1964. Even after recent strong Republican performances, political analysts still see Virginia as a battleground “purple” state. In 2012, the only question is whether it will have a reddish or bluish hue.

Before Webb’s announcement, a competitive Republican primary was already in place. So far, former Sen. George Allen, whom Webb defeated in an upset, faces Jamie Radtke, former chairwoman of the Virginia Tea Party Patriots. Democrats hope Ms. Radtke will push Mr. Allen to the right, allowing the Democratic nominee to occupy the middle.

A Democratic operative who knows Kaine would not rule out the possibility that Obama could coax him into the race. And “if he decides to do it, he’ll be all in,” said the Democrat.

If Kaine opts out, another possible Democrat would be former Virginia Rep. Tom Perriello, who lost reelection last November after serving one term. Usually, a defeated one-term former House member wouldn’t be seen as a strong Senate candidate, but Mr. Perriello had won in 2008 in a Republican district and had impressed national Democrats with his energy and fundraising skills. Given that the state overall is less conservative than the congressional district he represented, Perriello might actually have a better shot in a statewide Senate race than he did in his House race last fall. Still, he does not have the statewide profile of a Kaine or an Allen.

Allen was once seen as a top presidential prospect for the Republicans but saw his fortunes crumble in the 2006 campaign, when he was caught on video calling an Indian-American campaign volunteer for Webb “macaca,” an apparent racial slur. Webb went on to the win the race by just 9,329 votes.

Webb, too, is a competitive man, with the image of a fighter born of his years as a marine. (He also served as secretary of the Navy under President Reagan.) Some Democrats thought there was a decent shot that Webb would want to prove he could beat Allen again. But on Wednesday, his birthday, he put the speculation to rest.

"After much thought and consideration I have decided to return to the private sector, where I have spent most of my professional life, and will not seek reelection in 2012," Webb said in a statement. "Notwithstanding this decision, I have every intention of remaining involved in the issues that affect the well-being and the future of our country."

Webb’s announcement means there are now three Democratic-affiliated senators not seeking reelection. The others are Kent Conrad of North Dakota, whose seat could easily go Republican, and Joseph Lieberman of Connecticut, an independent who caucuses with the Democrats.

Democrats have an excellent shot at winning Senator Lieberman’s seat. But it’s a bad cycle for the Democrats: They are defending 23 seats; the GOP is defending only 10. The Democrats currently control 53 seats to the Republicans’ 47.